A research group led by Associate Professor Noriaki Ozaki of Hiroshima University Graduate School detected caffeine in storm water outflow pipes in urban areas with aging sewer pipes (sewage pipes) and discovered the possibility that leakage from sewer pipes is affecting the water quality of the storm water pipes.

 Currently, urban areas are designed to separate domestic wastewater from storm water drainage (separate sewerage system), but as the pipes deteriorate, rainwater and groundwater may flow into domestic drainage pipes, and conversely, domestic wastewater may leak into urban waters. In developed countries, including Japan, this infrastructure has been in use for more than 50 years, so deterioration and renewal are important issues.

 Although methods have been developed to diagnose drainage pipe leaks, such as direct observation with cameras, spot leak measurements, pipe condition monitoring, and tracer testing, the estimates of leakage rates vary widely. This is thought to be due to spatial and temporal variations in the underground environment, and research and survey methods to confirm these effects over a wide area have not been fully developed.

 The research group conducted monitoring using caffeine, flavoring substances, and polycyclic aromatic hydrocarbons as tracers in stormwater runoff pipes in five different urban areas, ranging from relatively recently constructed urban areas (approximately 10 years old) to urban areas that are more than 40 years old. They found that the older the urban area, the higher the concentration of caffeine in particular. The caffeine concentration in sewer areas that were more than 5 years old was at least two orders of magnitude higher than in sewer areas that were 40 years old, reaching a concentration equivalent to 10-2% of domestic wastewater, strongly suggesting that sewage pipes were leaking.

 These results point out the possibility that the deterioration of sewer pipes, which has become an issue in recent years, may already be affecting water quality downstream. Using this method, the researchers hope to clarify the impact on public water areas that is difficult to see.

Paper information:[Environmental Chemistry Letters] High caffeine levels in old sewer system waters reveal domestic wastewater leakage

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